A major problem in formulating detergent products for fabric washing by hand and in cool water, is the difficulty in reconciling the need for a highly effective detergency builders system which will adequately soften water during use under adverse washing conditions, which often also include low product dosage, with the fact that the users of such compositions cannot in general afford the most effective systems which would otherwise be desired. Nor indeed do the economies of the developing countries always permit the importation of large tonnages of foreign detergency builder materials such as sodium tripolyphosphate.
It has been proposed previously to use sodium carbonate as a detergency builder, and this material is widely available and relatively cheap. Unfortunately, however, sodium carbonate when used alone as the detergency builder does not function so effectively as would be desired, particularly at cool washing temperatures. Although the level of calcium ion concentration is lowered to a sufficient level by the presence of sodium carbonate, ie by precipitation of calcium carbonate, the precipitation process is a slow one and during the early part of the wash cycle the calcium concentration is higher than is desired for effective washing. During the initial period before the sodium carbonate is fully effective, there can be interaction between the calcium ions present and other ingredients in the detergent compositions. For example anionic detergent surfactants such as some sodium alkyl benzene sulphonates can be precipitated in the form of the calcium salts and this therefore contributes to a further reduction in detergency. Other types of detergent surfactants are known which are not precipitated by calcium ions, for example nonionic detergent surfactants, but these more sophisticated detergent surfactants tend to be more expensive, which mitigates against their use in the relatively cheap formulations.